The need for greater throughput and yield in the manufacture of semiconductor devices has driven the development and use of more highly automated wafer processing machines. Furthermore, the desire to reduce the particulate level to which the wafers are exposed during processing to as great a degree as possible has lead to the use of vacuum load locks and wafer transport mechanisms which operate in vacuum.
Typical prior art load lock devices employ sliding or rotating valves to isolate a single wafer. Such load locks require a pumpdown cycle for each wafer processed and thus inhibit throughput. In addition, prior art load locks are typically in-line devices; that is, wafers pass in a straight line through the load lock. This substantially contributes to the overall width of the wafer processing machine. Finally, prior art mechanical feedthroughs, which are used to transmit motion through a vacuum seal, have not been adequate to the task of simultaneously operating a load lock valve and indexing an internal wafer cassette.